Low solar factor (SF) and solar heat gain coefficient (SHGC) values are desired in some applications, particularly in warm weather climates. Solar factor (SF), calculated in accordance with EN standard 410, relates to a ratio between the total energy entering a room or the like through a glazing and the incident solar energy. Thus, it will be appreciated that lower SF values are indicative of good solar protection against undesirable heating of rooms or the like protected by windows/glazings. A low SF value is indicative of a coated article (e.g., IG window unit) that is capable of keeping a room fairly cool in summertime months during hot ambient conditions. Thus, low SF values are sometimes desirable in hot environments. High light-to-solar gain (LSG) values are also desirable. LSG is calculated as Tvis/SHGC. The higher the LSG value, the more visible light that is transmitted and the less amount of heat that is transmitted by the coated article. While low SF and SHGC values, and high LSG values, are sometimes desirable for coated articles such as IG window units and/or monolithic windows, the achievement of such values may come at the expense of sacrificing coloration and/or reflectivity values. In particular, conventional attempts to achieve low SHGC values have often resulted in undesirably low LSG values and/or undesirable visible coloration of the coating. It is often desirable, but difficult, to achieve a combination of acceptable visible transmission (TY or Tvis), low emissivity, desirable glass side reflective coloration (e.g., desirable a* and b* glass side reflective color values), low SHGC, and high LSG for a coated article in window applications, especially if it desired to use a glass substrate that is not deeply tinted.
SF (G-Factor; EN410-673 2011) and SHGC (NFRC-2001) values are calculated from the full spectrum (Tvis, Rg and Rf) and are typically measured with a spectrophotometer such as a Perkin Elmer 1050. The SF measurements are done on monolithic coated glass, and the calculated values can be applied to monolithic, IG and laminated applications.
Silver based low-E (low emissivity) coatings for windows are known in the art. However, silver is not particularly durable, and can be easily corroded if exposed to moisture for instance. Thus, silver based low-E coatings are not desirable for monolithic applications such as monolithic windows, and are typically used in IG window units including multiple glass panes, because of the durability problems of silver based low-E coatings.
Solar control coatings not based on silver are known, for example, having a layer stack of glass/Si3N4/NiCr/Si3N4/NiCr/Si3N4, where the NiCr layer may be nitrided. For example, see U.S. Patent Document 2012/0177899 which is hereby incorporated herein by reference. While layer stacks of U.S. Patent Document 2012/0177899 provide reasonable solar control and are overall good coatings, they are lacking in certain respects. The glass side reflective a* values (a* under RGY) in Examples 1, 4 and 5 in paragraphs 0025-0026 of US '899 are −17.8, −15.95, and +2.22, respectively. Examples 1 and 4 in US '899 are undesirable because the glass side reflective a* values are too negative at −17.8 and −15.95, respectively. And when RGY is reduced down to 15.82% in Example 5, this results in the glass side reflective a* color value in Example 5 becoming too red with a value of +2.22. Thus, the coatings described in US '899 were not able to achieve a combination of acceptable visible reflectivity values and glass side reflective a* coloration values.
It would be desirable according to example embodiments of this invention for a coating to be designed so as to have a combination of acceptable visible transmission (TY or Tvis), desirable glass side reflective coloration (e.g., desirable a* and/or b* reflective color values), desirably low film side visible reflectance, low emittance/emissivity, low SHGC, and high LSG for a coated article in window applications.
In certain example embodiments of this invention, certain applications such as monolithic window applications desire glass side reflective coloration that is not significantly red. In other words, certain applications such as monolithic window applications desire glass side reflective a* color values that are either negative or no greater than +1.6 or +1.0 (glass side reflective a* values higher than +1.6 are undesirably red). Such reflective a* values are especially desirable for example in the context of glass side reflective (RG[or outside, or exterior]Y) a* values.
Certain embodiments of this invention relate to coated articles that include two or more functional infrared (IR) reflecting layers that may be sandwiched between at least transparent dielectric layers, and/or a method of making the same. The dielectric layers may be of or include silicon nitride or the like. In certain example embodiments, at least one of the IR reflecting layers is of or including zirconium nitride (e.g., ZrN) and at least another of the IR reflecting layers is of or including indium-tin-oxide (ITO). It has surprisingly and unexpectedly been found that the use of these different materials for the different IR reflecting layers in a given solar control coating surprisingly results in improved optics such as improved glass side reflective a* values, low emittance, low film side visible reflectance, and/or high LSG values which are often desirable characteristics in window applications, and the provision of the IR reflecting layer of or including ITO allows coated articles to be more easily tailored for desired visible transmission values while the IR reflecting layer of or including ZrN can keep the normal emissivity, SF and/or SHGC values reasonably low and improve durability. Coating according to embodiments of this invention may be designed so that before and/or after any optional heat treatment such as thermal tempering the coated articles realize one or more of: desirable glass side reflective visible coloration that is not too red (e.g., reflective a* color value(s) from −14 to +1.6); a desirably low solar heat gain coefficient (SHGC); desirable visible transmission (TY or Tvis); desirably low film side visible reflectance; thermal stability upon optional heat treatment (HT) such as thermal tempering; desirably low normal emissivity/emittance (En); and/or desirably high light-to-solar gain ratio (LSG). Note that SHGC may be as high as 80% for uncoated glass. The higher the LSG value, the greater the energy saving. Such coated articles may be used in the context of monolithic windows, insulating glass (IG) window units, laminated windows, and/or other suitable applications.
In an example embodiment of this invention, there is provided a coated article including a coating supported by a glass substrate, the coating comprising: a first infrared (IR) reflecting layer comprising ITO on the glass substrate; a first dielectric layer comprising silicon nitride on the glass substrate over at least the first IR reflecting layer comprising ITO; a second layer IR reflecting layer comprising a nitride of zirconium on the glass substrate over at least the first dielectric layer comprising silicon nitride, so that the first dielectric layer comprising silicon nitride is located between at least the first IR reflecting layer comprising ITO and the second IR reflecting layer comprising the nitride of zirconium; a second dielectric layer comprising silicon nitride on the glass substrate over at least the second IR reflecting layer comprising the nitride of zirconium; wherein the coating contains no IR reflecting layer based on silver; wherein the coating has a normal emittance (En) value of no greater than 0.30; and wherein the coated article has: a visible transmission from about 15-80%, a film side visible reflectance no greater than 15%, a SHGC value of no greater than 0.45, a glass side reflective a* value of from −14.0 to +1.6, and a light-to-solar gain ratio (LSG) of at least 1.10.
In an example embodiment of this invention, there is provided a coated article including a coating supported by a glass substrate, the coating comprising: a first infrared (IR) reflecting layer comprising ITO on the glass substrate; a first dielectric layer comprising silicon nitride on the glass substrate over at least the first IR reflecting layer comprising ITO; a second layer IR reflecting layer comprising a nitride of zirconium on the glass substrate over at least the first dielectric layer comprising silicon nitride, so that the first dielectric layer comprising silicon nitride is located between at least the first IR reflecting layer comprising ITO and the second IR reflecting layer comprising the nitride of zirconium; a second dielectric layer comprising silicon nitride on the glass substrate over at least the second IR reflecting layer comprising the nitride of zirconium; wherein the coating contains no IR reflecting layer based on silver; wherein the coating has a normal emittance (En) value of no greater than 0.30; and wherein the coated article has: a visible transmission from about 15-80% and a light-to-solar gain ratio (LSG) of at least 1.17.
Thus, this invention covers monolithic window units, IG window units, laminated window units, and any other article including a glass substrate having a coating thereon as claimed. Note that monolithic measurements may be taken by removing a coated substrate from an IG window unit and/or laminated window unit, and then performing monolithic measurements. It is also noted that for a given coating the SF and SHGC values will be significantly higher for a monolithic window unit than for an IG window unit with the same coated article.